1. Field of the Invention
The present invention relates to a vacuum cleaner, and particularly to a vacuum cleaner which exerts suction without involving discharge of gas.
2. Description of the Background Art
Most conventional vacuum cleaners adopt the system in which dirt and dust particles are sucked up by a suction force produced as a fan attached to a motor rotates, where air is discharged as the fan rotates. It is therefore unavoidable that part of the collected particles are emitted with the discharged air and that the air blows off and scatters dirt and dust particles lying around it.
Some vacuum cleaners which manually create a vacuum adopt the system in which a suction inlet is attached to a flexible container which contracts and expands like an accordion, where the volume of the flexible container is manually expanded to create a low vacuum in the container, so that the pressure difference from the external pressure forces dirt and dust particles into the suction inlet. However, in this system, using the vacuum cleaner again requires contracting the flexible container again, in which process the internal air is discharged, causing the collected particles to escape or blowing off particles.
Motor-driven vacuum cleaners discharging a reduced amount of air are being developed in these days. They encounter no problem when used in ordinary environments, as in a house or an office; however, they cannot be used in extremely clean environments, such as a clean room in a semiconductor device manufacturing factory, because they still discharge a slight amount of air.
In a clean room, for example, a special cleaner is used which is designed to guide the discharged gas to the outside of the clean room. Such cleaners are large in scale and require equipment such as an air duct installed under the floor of the clean room.
According to a first aspect of the present invention, a vacuum cleaner comprises: a vacuum tank which is previously evacuated to create a vacuum with an evacuating system, the vacuum tank, after evacuation, being independent of the evacuating system and kept at a pressure lower than atmospheric pressure; a first valve connected to an opening of the vacuum tank, the first valve, when closed, keeping the vacuum tank airtight; and a suction unit defining a passage of gas which, when the first valve is opened, is sucked into the vacuum tank because of a pressure difference between the inside and outside of the vacuum tank.
Preferably, according to a second aspect, in the vacuum cleaner, the suction unit is connected to the first valve and the first valve has an adjustable opening, and wherein the suction force for sucking the gas into the suction unit is adjusted by adjusting the adjustable opening of the first valve.
Preferably, according to a third aspect, in the vacuum cleaner, the first valve is a gate valve in which the adjustable opening is adjusted by adjusting the area in which its gate valve element covers the adjustable opening.
Preferably, according to a fourth aspect, the vacuum cleaner further comprises a second valve provided upstream of the first valve in the passage of the gas and the second valve has an adjustable opening, wherein the suction unit is connected to the second valve and the suction force for sucking the gas into the suction unit is adjusted by adjusting the adjustable opening of the second valve.
Preferably, according to a fifth aspect, in the vacuum cleaner, the second valve is a gate valve in which the adjustable opening is adjusted by adjusting the area in which its gate valve element covers the adjustable opening.
The vacuum cleaner according to the first aspect of the present invention creates a suction force through a difference between the external atmospheric pressure and the pressure lower than the atmospheric pressure in the vacuum tank which is independent of the evacuating system, thus sucking up dirt and dust particles through the suction unit. The suction therefore does not involve discharge of gas at all and can be used in extremely clean environments. Furthermore, the structure for creating the suction force is formed just of the vacuum tank, providing a simply-structured compact vacuum cleaner.
According to the vacuum cleaner of the second aspect, the first valve is a valve which can be adjusted to adjust the state of the opening and the suction force for sucking the gas can be adjusted by adjusting the opening formed by the first valve. Accordingly, even though the volume of the vacuum tank is limited, the duration of the suction can be lengthened by adjusting the suction force.
According to the vacuum cleaner of the third aspect, the first valve is a gate valve which can provide a relatively large opening area and can be formed thinner in the direction of the gas passage. This offers a compact vacuum cleaner.
The vacuum cleaner of the fourth aspect comprises a second valve which is provided upstream of the first valve and can be adjusted to adjust the state of the opening, and a simply structured valve which is just opened and closed can be used as the first valve. When replacing the vacuum tank with a new one, the first valve and the vacuum tank can be removed/attached together from/to the second valve, which structure reduces the running cost.
According to the vacuum cleaner of the fifth aspect, the second valve is a gate valve which can provide a relatively large opening area and can be formed thinner in the direction of the gas passage. This offers a compact vacuum cleaner.
The present invention was made to solve the problem explained earlier, and an object of the present invention is to provide a vacuum cleaner which has a simple structure and exerts suction without involving discharge of gas at all so that it can be used in extremely clean environments.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.